The present invention relates to a process of, and apparatus for, treating and producing components for use as anodes and cathodes in electrolytic smelting plants.
In electrolytic smelting plants for furnaces producing aluminum, use is made of consumable carbon anodes and cathodes. Normally, the anodes and cathodes are formed as assemblies composed of blocks of carbon fixed to metallic support members. More particularly, the anodes, which are to be vertically displaceable during use, are composed of carbon anode blocks fixed to steel holders used to support the anode blocks and for supplying electrical current thereto. Similarly, the cathodes are composed of carbon cathode blocks fixed to busbars made, for example, from copper and used for supplying electrical current thereto.
To afix the aforesaid metallic members to the carbon blocks, it is usual to provide recesses in the carbon blocks which receive parts of the metallic members and to employ liquid cast iron poured into the recesses as grouting. During the smelting process, the carbon blocks are consumed. Although the anodic carbon blocks are consumed at a faster rate, the cathodic carbon blocks are also consumed. In order to save costs, it is desirable to strip off the carbon residues and to re-use the holders and busbars with fresh carbon blocks. To enable this stripping operation to be effected without damaging the holders and busbars, it is known to pre-coat these components with an agent, such as a water/graphite dispersion, to create a separation layer between the cast iron grouting and the metal surfaces. This agent is applied as a liquid or viscous substance to the connection zones of the holders and busbars prior to grouting. When the cast iron solidifies as an annular mass around the metallic holders and busbars, it does not directly contact the metal surfaces and hence subsequent separation is easier. The presence of water in the recesses of the carbon blocks and on the connection zones of the metallic members, i.e., the holders and busbars, is to be avoided in any event since, during grouting, bubbles of steam can create cracking or dispersions in the cast iron which can in turn lead to obvious difficulties. It is thus necessary to dry adequately both the recesses in the carbon blocks and the connection zones of the metallic members, especially when a pre-coating agent is applied, prior to grouting. Hitherto this drying step has taken a great deal of time and represents a production bottleneck, seriously affecting the efficiency of a continuous flow process. To promote the necessary drying, it has been known hitherto to place the components in question in a heating chamber heated by oil or gas burners. Primarily to accelerate the drying of the pre-coating or separation layer, it has also been known to expose the layer and also the recesses in the carbon blocks directly to combustion flames. This can involve considerable noise and discomfort to operators. In any event, this process is not wholly satisfactory, since uneven heating can result and the separation layer then cracks or burns. Discontinuities in the separation layer are disadvantageous, since the cast iron grouting can directly contact the metal surfaces and subsequent stripping of the cast iron is made more difficult. All the conventional drying operations involve considerable expense. In a typical plant, for instance, using oil as a fuel, sone 160 Kg of oil is consumed in one hour and, in addition, 4,000 liters of air are needed. The conventional drying operations are also inefficient, since a large proportion of the thermal energy is wasted.
A general object of the present invention is to provide an improved process of, and apparatus for, treating and assembling components as aforementioned.